424 cook: seedling morphology 



prophyllum and coleoptile 



The prophyllum of palms appears generally to be a double 

 organ, formed by the concrescence of bladeless sheaths repre- 

 senting the reduced leaves of two very short basal phyto- 

 mers of the inflorescence or the branch, in the few palms that 

 produce branches. Usually only the basal sheath of the in- 

 florescence shows the double or bicarinate condition, but in 

 inflorescences of the small, trunkless palms that constitute the 

 genus Sabal all of the spathes are compressed and bicarinate like 

 the first. 



Prophylla of grasses resemble those of palms except that they 

 are not united on the side away from the main axis, but this 

 condition also occurs in palms, having been observed in 1915 in 

 a Peruvian species of Ceroxylon. Here the sides not only failed 

 to meet in the middle but often the insertions were not directly 

 opposite. In grasses as well as in palms the prophylla are always 

 bicarinate and bilabiate, or biapiculate. Still more significant 

 facts have been noted by Mr. G. N. Collins, that when buds or 

 branches develop inside the prophylla their position is lateral, or 

 opposite one of the carinae, instead of in the median position that 

 would represent the axil if the prophyllum were a simple organ. 

 A few cases were found where two buds developed in the same 

 prophyllum, one on each side, a still more definite indication that 

 two metamers are represented. 



If it be admitted that the prophyllum is a double organ, indi- 

 cations of duplicity in the coleoptile do not require such an 

 interpretation as Worsdell' has proposed in homologizing the 

 coleoptile with the ligule of the foliage leaf. Metaphanic antici- 

 pation of a double organ like the prophyllum in the seedling 

 stage may be considered, or the alternative possibility that a 

 double organ of the seedling is reproduced in the prophylla of 

 the branches. A double coleoptile would mean that the leaves 

 of two primitive phytomers are involved, one probably the leaf 

 of the internode represented by the mesocotyl, the other a leaf 

 whose internode element has been suppressed. But whether 

 single or double, the coleoptile may be supposed to represent 

 the entire sheath of the foliage leaf, not merely the ligule. 



